16 



NERVOUS SYSTEMS AND SENSE ORGANS 



system. The four other muscles, the longitudinal muscles of the 

 stalk, proboscis and the two sets of the tentacles, are quicker in 

 their action and are controlled by anesthetics. These are probably 

 supjilied by sense cells and the nerve-net. 



Stimuli applied to any part of the normal animal may be trans- 

 mitted to distant parts; strong stimuli are transmitted to more dis- 

 tant parts than weak ones. The nervous transmission is probably 

 limited to the ectoderm. Although the nervous system is very 

 primitive, reactions much like a true reflex occur, as Parker has 

 pointed out. When a proximal tentacle is strongly stimulated ad- 

 jacent tentacles resjwnd and the proboscis may turn to the stimu- 

 lated point. 



Fin:. 4. A. General plan of the nevrous .system in Hydra. B. Nervous system 

 of Artiiiia. Diapramatic. C, D. Hydroid jellyfish showing position 

 of eye spots. Mayer. E, F. Otocysts of hydroid jellyfish, Mayer. 

 G. Otocyst and eye spot, Mayer. H. Hydroid medusa with eye spoU: 

 at base of tentacles. I. Tentaculocyst, Mayer. .1. Eye spot with 

 biconvex lens, Mayer. K. Tentacle and eye spot, Mayer. L. Diagram 

 of the nervous system of a hydroid jellyfish. Wall of the bell cut 

 away on one side showinp section of manubrium and gonad. M. Ten- 

 taculocyst and eye spot, Mayer. N. General plan of the nervous sys- 

 tem of a scyphozoan. Diapramatic. 



Many parts of the jiolyp are (juitc independent of the re.st of 

 the body, as may be seen when the hydranth has been removed; the 

 stalk will shorten and even localize a stimulus apjilied to one side. 

 The hydranth is not necessary for coordinated resjionse. Neither 



